This invention relates to the manufacture of dental restorations and more specifically to the fabrication of ceramic dental restorations and to the metallization of the internal surfaces of the ceramic restorations.
Fracture analyses of failed all-ceramic restorations reveal that the cracks typically initiate from their internal surfaces. These cracks may be initiated from the flaws that may develop from processing, etching or abrading of the ceramic surface that is required to improve the bonding between the ceramic and the tooth to which it is to be bonded. Use of resin-based adhesives in combination with resin based cements has been recommended to reduce such failures by providing an adequate bond between the cement and the ceramic and between the cement and the tooth. This has definitely improved the service life of the restorations. However, resin based adhesives and cements imbibe water. Therefore, the interface between resin adhesives and ceramics is not truly impervious to water. It is well known that mechanical properties of ceramics are lower in wet conditions. Also, it is to be noted that the moduli of these cements are lower than the moduli of the dentin or all-ceramic restorative materials. Therefore, crack-initiation and propagation may result from the combined effects of stress-corrosion at the interface and cyclic fatigue. Furthermore, the resin does not always fill in the crevices and surface etchings that result from the etching process and such crevices may lead to crack propagation.
To reduce or eliminate the cracking problems, porcelain-fused-to-metal (PFM) restorations have been fabricated whereby a metal core is manufactured and thereafter porcelain is fused to the metal core. The metal not only supports the porcelain veneer due to bonding and differential contraction but also offers an impervious layer for fluid penetration. Also it is conventional to use zinc phosphate or non-resin modified glass-ionomers cements for cementation of these PFM restorations. Interestingly, the moduli of such cements are higher than that of the resin-based alternatives.
It is desirous to eliminate the lost wax process and create a more efficient and simplified process for the manufacture of a dental restoration. It is beneficial to reduce the amount of metal employed in the manufacture of dental restorations to provide a more aesthetic appearance. Dental practitioners also prefer not to use resin-based adhesives/cements as they are time consuming and technique sensitive.
These and other objects and advantages are accomplished by the materials and methods of the present invention comprising a ceramic core material having a thin metallic layer disposed on the interior surface of the ceramic core to provide integrity to the ceramic core, eliminate bonding between the ceramic core and the patient""s tooth or teeth, and provide an impervious layer on the ceramic interior to reduce infiltration of fluids into the ceramic and reduce cracking of the ceramic restoration. The metallic layer may comprise a metal, alloy or metal-matrix ceramic material.
In one embodiment of the method of the invention, the ceramic core structure is fabricated. Thereafter, the metallic layer is applied to the interior surface of the ceramic core by known techniques such as electrolytic or electroless deposition, sol/gel deposition followed by pyrolysis, fusing (sintering), pressing, sputtering, chemical vapor deposition, ion bombardment, and vacuum deposition.
In another embodiment of the method herein, a metal or metal-matrix ceramic material is first formed into a thin core structure. Thereafter, a ceramic material is applied to the thin layer of metal or metal-matrix ceramic material by known techniques such as electrolytic or electroless deposition, sol/gel deposition followed by pyrolysis, fusing (sintering), pressing, sputtering, chemical vapor deposition, ion bombardment, and vacuum deposition.
A strong, crack-resistant ceramic restoration is provided having highly aesthetic properties.